1. Field of the Invention
The present invention generally relates to twisted pair exchange cables, and, more particularly, to an improved process and apparatus for producing twisted pair exchange communication cables.
2. Description of the Related Art
Telecommunication networks commonly use twisted pair exchange cables to transmit voice and data signals between central offices and the individual end users. A twisted pair exchange cable comprises groups of individual conductor wires that are twisted together into pairs. A twisted pair exchange cable may have 50, 100, 1200, 2400 or any number of pairs contained in one cable.
For economy of manufacture, it has long been the practice to group a large number of conductor pairs into units within one cable; each unit typically contains 50, 100 or any convenient number of conductor pairs. To facilitate efficient manufacturing and installation, it is often necessary to identify a particular unit within the cable. For example, if the cable is accidentally severed and needs repairing, then the two parts of the cable may be restored by splicing together the corresponding twisted pairs. Splicing a cable requires the cable splicer to identify the corresponding units of conductor pairs within each part of the cable that is to be spliced. Complete color coding of each conductor pair within a telecommunications cable requires such a vast inventory of colors as to make complete color coding impractical. If each conductor pair had a unique color code, then the distinction between color shades of separate conductor pairs would be imperceptible to the human eye due to the large number of different colors that would be required. It is has therefore become standard practice in the industry to only uniquely color code conductor pairs within a unit. Thus, it is only necessary to uniquely color code units within a cable so that a cable technician can identify the corresponding units within each part of the cable that is to be spliced.
A color coding system for units within a cable is disclosed by Nutt et al., U.S. Pat. No. 4,128,736, issued Dec. 5, 1978. Nutt et al. disclose a mirror image coding system for 100 or 50 conductor pair units. Each unit is held together by two separately colored ribbons that serve to uniquely identify the unit based on its orientation within the cable. Hence, a cable technician can use the colored ribbons to identify two compatible units in separate pieces of cable for splicing. This color coding greatly simplifies the work of the cable tester, installer, splicer, and maintainer.
Current processes that are used to manufacture twisted pair exchange cables are generally divided into two phases: stranding and cabling. During the stranding phase, the unit is assembled from smaller sub unit components that contain a smaller number of conductor pairs. For example, a unit with one hundred conductor pairs may be constructed from four sub units that each have twenty five conductor pairs. When the four sub units are combined together to form the unit, they are twisted together and the two colored ribbons are applied. The two colored ribbons then serve to uniquely identify the unit. The units that are created during the stranding phase are stored on large spools which are referred to as unit trucks.
During the cabling phase, the final twisted pair exchange cable is constructed from the units produced by the stranding phase. This is accomplished by assembling the units together, in their proper orientation, to form the twisted pair exchange cable. The particular orientation of units within a given cable may be dictated by one or more cable standards. The output of the cabling phase will result in a twisted pair exchange cable that often has 1200 or more conductor pairs.
It is well known in the art that the two colored ribbons that serve to identify a unit are applied at the same time during the stranding phase. This will result in units that have different combinations of color ribbons. Hence, the different colored units need to be tracked separately from the stranding phase through the cabling phase.
Tracking the separate units adds complexity and cost to the manufacturing of twisted pair exchange cables. It adds complexity because there are numerous different color coded units that need to be tracked separately. These separate units need to be transported from the stranding machine to the machines used for the cabling phase. At the start of the cabling phase, each unit is loaded and strung so that it is in the correct orientation with respect to its color coding and the configuration of the twisted pair exchange cable that is to be produced. For a cable that requires 10-12 units or more, this is a time-consuming process that could take several hours. Thus, product changeover time can be quite long, since different twisted pair exchange cables often require different color combinations of units. Each time a different combination of units is required, the units that are the source for the cabling phase have to be changed. As stated above, this is a process that takes several hours. Thus, one shortcoming of the prior art is the lengthy product changeover time that is required when different twisted pair exchange cables are manufactured.
Since product changeover time is long, orders for small quantities of exchange cable (short orders) are expensive to fill. A short order is an order for a quantity of cable that is less than the amount of cable on a standard unit truck. A short order will entail changing the units that are used during the cabling phase, unless there is more than one short order with the exact same unit configuration. The units that are changed out will have to be tracked, and, if possible, used to fill other short orders. This rapidly adds complexity to the tracking of units, because the inventory of units will quickly build up with units of various lengths of cable. This often means that units are discarded without being fully used up, thus adding cost to the manufacturing of cables. Therefore, another shortcoming of the prior art is that the filling of short orders is expensive, and thus are not economically feasible to fill.
Another shortcoming is the complexity of the binding machines that are used to apply the colored ribbons to the units. Currently, it is well known in that art that there can be two spindles per drive belt of the binding machine. The spindles are used to apply the colored ribbons to the units of cable. Thus, for example, if eighteen spindles are desired to be used, then nine drive belts would be required. This creates complexity and makes maintenance of the machine more difficult which ultimately results in increased cost. Thus, it would be desirable to have a binding machine that allows for more spindles per drive belt which reduces the number of drive belts that are required. Another shortcoming of the binding machines of the prior art is that spur gears are often used to rotate the spindles. However, spur gear drives are noisy and expensive to maintain. Thus, it would also be desirable to have a cabling machine with a different mechanism for driving the spindles that is less costly to maintain.